Liquefaction Susceptibility Assessment of Oil Sands Tailings
Abstract
Canada has the world’s third-largest crude oil reserve, with an estimated recoverable oil reserve of 171 billion barrels (10.3% of world proven oil reserve). However, this is primarily stored in oil sands deposits and should be extracted through mineral processing. The remaining tailings following the extraction of bitumen from oil sands consists of sands, fine particles, water, and residual bitumen, which is deposited behind a tailings dam. Tailings dams are particularly susceptible to liquefaction and exhibit a strength loss when loaded without allowing their volume to change in loose saturated conditions. A tailings dam must withstand both static and seismic loads to remain stable for a very long time. Lateral stress relief and effective stress reduction also have been recognized as the culprits in flow failures of several mine tailings dams and can be simulated in the laboratory as drained constant shear unloading (DCSU) tests. This research examines the instability of coarse oil sands tailings (CST) in both constant volume (CV) and DCSU stress path through a series of monotonic direct simple shear tests. A detailed investigation is carried out to observe the cyclic, post-cyclic liquefaction behaviour and dynamic properties of coarse oil sands tailings (CST). A tailings dam is made up of coarse sands tailings (CST) and fluid fine tailings (FFT), which can be mixed in various quantities and have significantly different properties than either CST or FFT. Laboratory specimens were prepared using moist-tamping (MT), dry deposition (DD), and slurry deposition (SD) techniques to investigate the effect of sample reconstitution method and tailings fabric on CST’s instability behavior. The effects of consolidation stress, void ratio, initial shear stress, and unloading rate on the drained instability of CST specimens were also investigated. The effectiveness of a naturally driven biological process known as microbially induced calcite precipitation (MICP) on the monotonic and cyclic shear response of oil sands tailings is also assessed. Sporosarcina pasteurii is employed to precipitate calcite (CaCO3) by its metabolic action to alter the engineering properties of CST.